Due to its good mechanical properties, dimensional accuracy and electrical properties, etc., the polycarbonate resin is used in a variety of applications ranging from industrial fields, such as the electrical/electronic equipment field, the office automation (OA) equipment field and the automotive field, to groceries, medical supplies, security products and entertainment products. In recent years, particularly in the fields centered on the electrical/electronic equipment and the OA equipment, with wall thinning of the molded article for cost reduction or weight reduction, higher flame retardance is needed for the polycarbonate resin. Moreover, to obtain a molded article having a thin wall, the molding temperature of the polycarbonate resin composition is set at a high temperature.
Polytetrafluoroethylene (sometimes called “PTFE” hereinafter) has the characteristic of fibrosis through a minor stress due to its high crystallinity and low intermolecular force. Therefore, by mixing PTFE in a resin and fiberizing the same, melt tension can be provided to the resin. As a result, falling of flame drops when the resin is burnt is suppressed to suppress spreading of the burning. Therefore, previously, PTFE and a flame retardant were used together as an additive for various resins represented by polycarbonate resin.
The compatibility of PTFE with almost all thermoplastic resins is poor, and if PTFE is only added in a resin composition and simply blended, the PTFE is not readily uniformly dispersed in the resin composition. As a result, PTFE aggregates are readily formed in the resin composition, causing the appearance of the formed article to be poor and increasing the addition amount needed for the flame retardance performance. If the content of PTFE is increased in the resin composition, mechanical properties such as impact resistance of the molded article are reduced. Thus, a resin modifier containing PTFE and an organic polymer is used such that the PTFE can be dispersed in the resin composition in a satisfactory manner.
However, when the resin composition is molded under high temperature, the issue of compromise to the appearance or the flame retardance, etc. of the molded article due to byproducts remaining in the resin modifier or thermal decomposition of the organic polymer is present. As a result, improvement of thermal stability of the resin composition when molded under high temperature is an important topic.
Moreover, from the perspective of reducing environmental burden, a polycarbonate resin composition still having good flame retardance in a molded article having a thin wall without use of the prior bromine-based compound or phosphorus-based compound used as the flame retardant is also in strong demand.
In a method without using a bromine-based or phosphorus-based compound, a resin composition (Patent Document 1) in which a mixture of an organic sulfonate metal salt, an acrylic acid-based resin, and PTFE is prepared and used in a polycarbonate resin is proposed. However, in the method recited in Patent Document 1, since the acrylic acid-based resin does not contain an aromatic vinyl monomer unit, the thermal stability of the resin composition may be insufficient when molded under high temperature.
Moreover, in a method in which the reduction of hydrolysis resistance or thermal stability of the polycarbonate resin composition caused by byproducts in the resin modifier is suppressed, a resin composition (Patent Document 2), which is obtained by mixing in a polycarbonate resin a rubber-modified graft polymer that is formed with polymerization in the presence of an alkali metal salt of a saturated fatty acid, is proposed. However, in the method recited in Patent Document 2, since a sulfate salt is used in the latex of the rubber-modified graft polymer when the polymer solid content is recycled as a powder, the thermal stability of the resin composition may be insufficient when molded under high temperature.